The present invention relates to a flexible hose comprising a peripheral rubber wall and a linear reinforcement of rigid resin for reinforcing the rubber wall.
Generally rubber hoses reinforced with a rigid resin linear reinforcement are more advantageous in resistance to oil, to heat and to abrasion than hoses comprising a peripheral wall of soft polyvinyl chloride resin reinforced with a helical linear reinforcement of rigid polyvinyl chloride resin because of the properties of rubber. With hoses of the latter type, the plasticizer contained in the soft polyvinyl chloride resin tends to migrate into the rigid polyvinyl chloride resin, reducing the rigidity required of the reinforcement and resulting in cracks in the reinforcement, whereas rubber hoses are free of such degradation attributable to the plasticizer but it is extremely difficult and industrially not feasible to ensure a rigid bond between the dissimilar materials used, namely between the rubber and the rigid resin.
A method has been proposed of producing rubber hoses by helically winding a rigid resin linear reinforcement around an unvulcanized rubber tube, covering the reinforced tube with a layer of unvulcanized rubber or with a fabric impregnated with unvulcanized rubber, and heating the resulting assembly for vulcanization to intimately join the inner and outer rubber layers together and to fuse the reinforcement to the two rubber layers with the heat of vulcanization. However, this method gives no consideration to strengthen the bond between the rubber and the rigid resin which are inherently difficult to bond together. In fact, the reinforcement is merely interposed between and held by the inner and outer rubber layers by virtue of the rubber-to-rubber bond of the two layers. Futher because the inner rubber layer, the reinforcement and the outer rubber layer are not produced at the same time and because the reinforcement is gripped between the inner and outer rubber layers, it is difficult to wrap up the reinforcement with homogeneous rubber over the entire periphery thereof, and a weak point is liable to occur on the peripheral surface of the reinforcement at the interface between the inner and outer rubber layers.
These objections invariably lead to the drawback that when the hose is repeatedly bent and deformed, the reinforcement tends to separate from the surrounding rubber portion, failing to afford the contemplated pressure resistance, tensile strength and like reinforcing effects. Thus, it has been desired to remedy this drawback.
The present invention has overcome such problem.